There is another annoying little bug I've been meaning to mention for some time:

If you try to draw an Arc by Diameter, say on the end of two lines, and those two lines are within a polygon or a polycurve, then it won't do it. See below:

Screen Shot 2017-10-19 at 09.23.35.png (15.53 KiB) Viewed 532 times

On the above, you can draw the Arc by Diameter coloured blue on the end of the two lines (red and black) outside the polygon (highlighted). But if you try to the same on the two ends within the polygon, you get the anomalous result shown in red - the arc draws somewhere else (I assume related to the polygon?).

The only solution I've found is to convert the polygon to lines - which is a pain and not easy if there are a lot of curves – or move the bits you want to draw the Arc by Diameter on to a new layer, and then move them back again once you have drawn the arc. Neither are particularly good options!